<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>对象-可选链操作符-ES11</title>
</head>

<body>
  <script>
    // ?.
    function main(config) {
      // const dbHost = config && config.db && config.db.host;
      const dbHost = config?.db?.host;

      console.log(dbHost);
    }

    // main({
    //   db: {
    //     host: '192.168.1.100',
    //     username: 'root'
    //   },
    //   cache: {
    //     host: '192.168.1.200',
    //     username: 'admin'
    //   }
    // })

    main();

  </script>
</body>

</html>